South Carolina's Marcus Lattimore was college football's best running back in the autumn of 2011, combining speed, vision and power to devastating effect and a per-carry average of 5.5 yards to go with 11 touchdowns through the first seven games of the season. He was headed for a first-round selection in the NFL Draft, and the millions of dollars that come with that.

On Wednesday, Lattimore announced his retirement from the game he dedicated his life, hopes and dreams to. He was 23 years old and never played a down in the NFL.

What happened in the three years between those two events? A catastrophic knee injury is the easy answer. But what really happened? Lattimore's dreams, career and lucrative livelihood were robbed from him by the NFL's rule that promising players can't be drafted until they're at least three years out of high school.

The moment that changed Marcus Lattimore's life forever came on Oct. 27, 2012 — but it didn't have to come at all.

After the 2011 season Lattimore had — as they say in the industry — nothing left to prove. He'd already shown that his skill and athleticism made him an ideal NFL feature-back, one NFL scouts and general managers drooled over in games and on film.

But 2011 was only Lattimore's sophomore year, you see, so the NFL was off-limits. He returned to South Carolina for the 2012 season, to again offer his star power and unpaid labor as a centerpiece of the NCAA's billion-dollar enterprise that's long since outgrown the "amateurism" trope of major college sports.

Lattimore, of course, dominated again in 2012. Then, on Oct. 27: disaster. Against the Tennessee Volunteers, Lattimore suffered a catastrophic knee injury.

It was the kind of injury that lights up Twitter, makes stomachs churn and puts fans in a schizophrenic mess about whether or not to watch the replay of a human limb being forced to bend in the exact opposite direction it was intended to. He tore up both the anterior cruciate ligament and lateral collateral ligament in his right knee.

You can take our word for how gruesome the injury was, or — if you must — watch it right here.

So there was Marcus Lattimore in the fall of 2012. Instead of collecting a fat pay check playing against players he could definitely hang with, his right knee was mangled and his professional career was very much in doubt.

Yet the San Francisco 49ers took a chance on him anyway the next April, selecting him in the 2013 NFL Draft's fourth round. According to ESPN's Darren Rovell, the team gave Lattimore a $300,000 signing bonus but likely didn't have to pay him what would have been his regular salary because he was placed on an injured-reserve list. Let him rehab his injury, the 49ers thought, and bet that he'd eventually return to form.

Marcus Lattimore was drafted by the 49ers but never played an NFL down.

Image: File photo/Associated Press

After two years of rehab work, though, Lattimore decided the recovery process was "insurmountable." He announced his retirement with a Wednesday afternoon tweet.

“I have given my heart and soul to the game that I love, and it’s time for me to move on to the next chapter of my life and help others," read the statement he posted online. "I have given every ounce of my energy toward making a full recovery from my knee injury, and I have made a lot of progress. Unfortunately, getting my knee fully back to the level the NFL demands has proven to be insurmountable."

Lattimore reportedly had a $1.7 million insurance policy to help protect him against just this kind of result. He's by all accounts a smart, hard-working guy. In short, Marcus Lattimore will be fine in life — but it's impossible not to think of what might have been if he'd been allowed to ply his trade when he was ready, not when rules said it was OK.

Had Lattimore designed a killer app, or been a cello prodigy, he could have left school and gone pro as a developer or musician.

Lattimore had a teammate named Jadeveon Clowney at South Carolina, a dominating defender one year younger than him. Clowney would have been the top pick in the 2013 NFL Draft, but couldn't come out because, again, he was just two years out of high school at the time (stop us if this sounds familiar).

So Clowney returned for his junior season, during which he drew widespread criticism from many for loafing, taking plays off and generally not playing as hard as he could have.

Clowney is selfish, the thinking went. How could he shortchange his college teammates and fans by prioritizing health and a future pro career? How he could be so disloyal? What gives him the right?

Clowney avoided injury his junior year, was the top pick in the 2014 NFL Draft and signed a multiyear deal with $22 million guaranteed. If Clowney did in fact slack off during his third and final college season to protect his pro prospects, you sure can't blame the guy.

It doesn't take a college degree to figure that one out.

2014's Most Unforgettable Sports Moments

1. Richard Sherman goes off

After Richard Sherman's Seattle Seahawks beat the 49ers in January to reach Super Bowl XLVII, he went on an epic, trash-talking rant in a post-game interview. That led to a two-week news cycle of all Sherman, all the time, but he had a message for the haters.

Image: Elaine Thompson/Associated Press

2. Super Bowl? Super blowout

Super Bowl XLVII was supposed to be a classic matchup between the up-and-coming Seahawks and Peyton Manning's Denver Broncos. Instead, it was an all-time blowout, leading to shock, awe and memes aplenty. Maybe we'll get a rematch this coming February?

Image: Paul Sancya/Associated Press

3. #SochiProblems

Sochi, Russia, was woefully unprepared to host flocks of journalists traveling there to cover the Winter Olympics in February. Reporters tweeted their still-unfinished accommodations, the #SochiProblems hashtag took on a life of its own, a parody account was born and some of us got a little tired of the whole whine-fest.

Image: Pavel Golovkin/Associated Press

4. UConn's Cinderella run

An undersized scoring guard, a second-year coach, a seven-seed -- the UConn Huskies were not supposed to win the 2014 edition of March Madness. Yet, that's exactly what they did -- in entertaining, exhilarating and inspiring fashion, no less.

Image: Seth Wenig/Associated Press

5. NBA owner's racist bombshell

The world reacted in shock in April when audio was leaked of Los Angeles Clippers owner Donald Sterling making a string of racist comments -- even though some of us weren't so surprised. Powerful player statements came next. Then months of legal wrangling, but the NBA finally got rid of Sterling, and former Microsoft CEO Steve Ballmer now owns the team.

Image: Mark J. Terrill/Associated Press

6. Luis Suarez takes a bite out of the World Cup

Luis Suarez had bitten before. But on the biggest stage, in a World Cup match against Italy? Yup, the Uruguayan star tried to chomp an Italian defender, setting the web aflame, as fans reveled in the absurdity. He's banned from playing for club team FC Barcelona until January.

Image: Ricardo Mazalan/Associated Press

7. Germany breaks Brazil's collective heart

Germany absolutely obliterated host Brazil in the World Cup semifinals on July 8, shocking soccer fans across the globe with a 7-1 win. Brazil captain David Luiz then gave a heartbreaking TV interview, and the entire nation had to reconsider its place in the global soccer pecking order.

Image: Felipe Dana/Associated Press

8. LeBron returns home, sweet home

Ohio native LeBron James crushed Cleveland's dreams when he left the Cavaliers for the Miami Heat as a free agent in 2010. This free agency go-round, King James left Miami to return to Cleveland in July. Can he deliver his home state an NBA title? Only time will tell, but one thing is certain: It's going to be fun to watch.

Image: Tony Dejak/Associated Press

9. Tony Stewart kills Kevin Ward, Jr. on the racetrack

NASCAR superstar Tony Stewart struck and killed a young driver named Kevin Ward, Jr. in a sprint-car race in August after Ward exited his vehicle to confront Stewart following a testy exchange on the track. This prompted speculation about whether Steward intended to hit Ward, and caused the star to miss some races. He was ultimately cleared, but it remains a truly shocking story.

Image: Mike Groll/Associated Press

10. The NFL implodes

The NFL faced perhaps its worst moment in September when a string of domestic violence cases shed an unflattering light on the way the league disciplines and handles such crimes. Commissioner Roger Goodell gave a cringeworthy news conference to address the mess, which is still playing out, and is far from over. This story is a fascinating one that will surely carry over well into 2015.

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